The invention relates to a rotary drill bit for the drilling of wells in subterranean formations. The invention relates in particular to a rotary drill bit that is furnished with a tubular strainer element for the cleaning of drilling fluid flowing from a drill string connected to the bit to jet nozzles arranged in the bit. Such a bit is known from U.S. Pat. No. 4,341,273. In the bit known from that patent specification, the tubular strainer element is placed in such a manner that during drilling at least some of the drilling fluid flows out of the drill string in a substantially axial and downward direction through the space enclosed by the strainer element. In the wall of the strainer element, a number of fluid passages are arranged that lead into a space situated at the outside of the element, which space communicates with the jet nozzles. The fluid passages consist, at least at the fluid inlet side situated on the inside of the element, of substantially axially oriented slots.
In the known bit, the width of the axial slots is selected so that any solid particles present in the drilling fluid of such size that they could block the jet nozzles cannot pass through the slots and are entrained in the drilling fluid flowing in an axial and downward direction through the space enclosed by the strainer element to a central drilling fluid discharge port arranged in the bit, which port may consist of a central nozzle of a diameter selected large enough for the solid particles that cannot pass through the slots to be discharged from the space enclosed by the strainer element via the central nozzle. In the known bit, the purpose of the axial orientation of the slots is that the thereby intercepted solid particles are not sucked up against the inner wall of the strainer element by the radial flow through the slots but are flushed away from it by the axially and downwards directed flow. The flushing away of the solid particles implies that the strainer has a self-cleaning action.